diff --git a/grub-core/lib/crypto.c b/grub-core/lib/crypto.c
index e6f55062b..5098f0a66 100644
--- a/grub-core/lib/crypto.c
+++ b/grub-core/lib/crypto.c
@@ -345,7 +345,8 @@ grub_crypto_hmac_init (const struct gcry_md_spec *md,
 }
 
 void
-grub_crypto_hmac_write (struct grub_crypto_hmac_handle *hnd, void *data,
+grub_crypto_hmac_write (struct grub_crypto_hmac_handle *hnd,
+			const void *data,
 			grub_size_t datalen)
 {
   hnd->md->write (hnd->ctx, data, datalen);
diff --git a/include/grub/crypto.h b/include/grub/crypto.h
index ab82da862..baccbcd06 100644
--- a/include/grub/crypto.h
+++ b/include/grub/crypto.h
@@ -235,7 +235,8 @@ struct grub_crypto_hmac_handle *
 grub_crypto_hmac_init (const struct gcry_md_spec *md,
 		       const void *key, grub_size_t keylen);
 void
-grub_crypto_hmac_write (struct grub_crypto_hmac_handle *hnd, void *data,
+grub_crypto_hmac_write (struct grub_crypto_hmac_handle *hnd,
+			const void *data,
 			grub_size_t datalen);
 gcry_err_code_t
 grub_crypto_hmac_fini (struct grub_crypto_hmac_handle *hnd, void *out);